The invention relates to the field of control and instrumentation technology for gas turbines. It relates to a method and a computer program product for determining a degradation of a gas turbine.
Such a method for determining a degradation of a gas turbine is known, for example, from xe2x80x9cAn Object-Oriented Diagnostic Computer Program Suitable for Industrial Gas Turbinesxe2x80x9d, P.C. Escher et al., CIMAC Conference, Interlaken, Switzerland, May 15-18, 1995, the content of which is hereby incorporated in the application. In this method, a degradation state of a gas turbine is determined with the aid of measurements during operation of the gas turbine. The method, termed GPA (xe2x80x9cGas Path Analysisxe2x80x9d), uses a mathematical simulation or a model of a thermodynamic and aerodynamic operating behavior of the gas turbine. The model permits values of measurable output variables to be determined from input variables such as, for example, air inlet temperature and pressure, as well as from assumptions concerning state parameters. Such output variables are, for example, pressures, mass flows and temperatures at various points in the gas path of the gas turbine, a fuel mass flow, a rotational speed and an output mechanical power. Individual state parameters represent a degradation state of respectively one component of the gas turbine, for example a contamination of compressor blades and a reduction in swallowing capacity of the compressor, erosion of turbine blades or corrosion of machine parts.
In order to be able to plan maintenance of the gas turbine, it is of interest to know as early as during the operation of the gas turbine the state in which the individual components are to be found. Since the state parameters are not measurable, they are deduced with the aid of measured values of the measurable output variables and with the aid of the model.
The problem arises in this case that sensors can be defective and can supply wrong measured values. The estimated state parameters are also falsified thereby, and it is not immediately evident whether a variation of measured values is to be ascribed to a change in the state or a falsification of the measured values by a defective sensor. The existing methods (for example method of least squares) have the disadvantage that either redundant sensors must be used or that the possibility of detecting a sensor defect is limited by the lack of knowledge of the observed process, and this is attended by a high outlay on engineering.
It is therefore an object of the invention to create a method and a computer program product for determining a degradation of a gas turbine of the type mentioned at the beginning which permit simple determination of defective measured values and sensors.
Thus, according to the invention a degradation state of the gas turbine is repeatedly estimated with the aid of a set of measured values, at least one of the measured values not being taken into account in each case during the estimation. A deviating estimate which deviates substantially from the remaining estimates or from an estimate which takes account of all the measured values implies that a measured value which has not been taken into account for this deviating estimate is defective.
This renders it possible to distinguish in a simple way between changes in state and measuring errors. In the case of a GPA method for determining a degradation of a gas turbine which is being implemented in any case, the determination of defective sensors according to the invention is possible with a low programming outlay and without assumptions concerning a response of individual sensors.
A further advantage is that the method uses a large quantity of information, that is to say data from a plurality of sensors and information concerning a response of the gas turbine. This raises the quality of the method by contrast with methods which judge a sensor in isolation, that is to say only with the aid of its own measured values.